I thought that XP4 was given (for free) to a relative of Bruce McLaren in the states and Blair looks after the car for him. Also, small bits of DA make me believe that XP2 was never written off and was used as a development car right up to when production started. Check out the thread "Fate of the XPs" for more info.
BTW: The hitasuma (or whatever) car is down on JGTC team lists as 019R, which obviously can't be true.